Set specific address sub field from another field

Does anyone know how to set a specific sub field of the address field from another field that is not an address field?

Example:
I have a number field that I ask a user to enter their Zip Code. I want to copy that value into the Zip Code "sub" field of the address field. Is that possible?

Reason:
I want to use that Zip Code with the Map Feature, so it must be in the Address Field (I think?)

Thanks Tony, that worked!